Fan speed control system

ABSTRACT

A fan speed control system. A temperature and humidity sensing unit detects environmental temperature and humidity and outputs a corresponding electrical signal. A micro-control unit receives and processes the electrical signal to obtain a digital signal, and sends the digital signal to the fan motor circuit to control fan speed accordingly.

BACKGROUND

The present invention relates to a speed control system for fan, and particularly to a speed control system for fan responding to environmental temperature and humidity.

Fans are widely used for heat dissipation in electrical devices. Generally, fan speed is modulated by a speed control circuit responding to environmental temperature. The speed control circuit is typically driven by pulse width modulation (PWM) signals or voltages. Humidity, however, is not considered a factor in modulation of fan speed in the speed control circuit. When an electrical device with the speed control circuit is operated in low environmental temperature and high humidity, fan speed is not increased due to the low temperature. However, moisture may adhere to elements of the fan and the electrical device, resulting in short-circuit or rust that contaminates or damages the electrical device.

SUMMARY

Accordingly, an embodiment of a fan speed control system comprises a fan motor circuit, a temperature and humidity sensing unit, and a micro-control unit. The temperature and humidity sensing unit sends an electrical signal related to detected temperature and humidity. The micro-control unit receives and processes the electrical signal to obtain a digital signal, and sends the digital signal to the fan motor circuit to control speed thereof.

The temperature and humidity sensing unit can comprise heat-sensitive and humidity-sensitive resistors, and the digital signal can comprise a pulse width modulation (PWM) signal.

A detailed description is given in the following embodiments with reference to the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

FIG. 1 is a block diagram of a fan speed control system of an embodiment of the invention; and

FIG. 2 is a schematic view of the temperature and humidity sensing unit in an embodiment of the present invention.

DETAILED DESCRIPTION

In an embodiment of the invention, a fan speed control system responding to environmental temperature and humidity is provided in an electrical device. In some embodiments, moisture can be prevented from contacting elements of the electrical device and the fan thereof.

FIG. 1 is a block diagram of an embodiment of a fan speed control system 2, comprising a temperature and humidity sensing unit 21, a micro-control unit (MCU) 22, and a fan motor circuit 23.

The temperature and humidity sensing unit 21 detects temperature T and humidity H in the operating environment, and sends an accordingly generated electrical signal S₁ to MCU 22 comprising one electrical signal for temperature T, and one for humidity H. The MCU 22 receives and processes the electrical signal S₁ to obtain a digital signal 221, such as a pulse width modulation (PWM) signal, and sends the digital signal 221 to the fan motor circuit 23 to control fan speed V.

Further, the fan speed control system in the embodiment comprises a speed sensing unit 24, which detects fan speed V and sends an electrical signal S₂ therefore to the MCU 22, which compensates digital signal 221 accordingly. Thus, fan speed V achieves a desired value with the feedback control of the electrical signal S₂.

FIG. 2 shows the temperature and humidity sensing unit 21, comprising a temperature sensing element 211, a humidity sensing element 212, and resistors 213 and 214. The temperature sensing element 211 can be a heat-sensitive resistor, and the humidity sensing element 212 can be a humidity-sensitive resistor.

The temperature and humidity sensing unit 21 further comprises a voltage input terminal 215 and two signal output terminals 216. The voltage input terminal 215 is connected to a power source V_(in), and the signal output terminals 216 are connected to the MCU 22.

The signal output terminals 216 transfer electrical signals S11 and S12 from the temperature sensing element 211 and the humidity sensing element 212. The signal output terminals 216 obtain terminal voltages from the heat-sensitive resistor of the temperature sensing element 211 and the humidity-sensitive resistor of the humidity sensing element 212 as electrical signals S11 and S12. Resistance R1 of resistor 213 and resistance R2 of resistor 214 can be modulated in accordance with the resistances of the heat-sensitive resistor and the humidity-sensitive resistor.

According to the embodiment, the speed control system 2 controls fan speed V of the fan according to environmental temperature and humidity. Embodiments of the invention may thus contribute to prevention of overheating and condensation.

While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements. 

1. A fan speed control system, comprising: a fan motor circuit; a temperature sensing element detecting environmental temperature and sending a corresponding first electrical signal; a humidity sensing element detecting environmental humidity and sending a corresponding second electrical signal; and a micro-control unit receiving and processing the first and second electrical signals to obtain a digital signal, and sending the digital signal to the fan motor circuit to control fan speed.
 2. The fan speed control system as claimed in claim 1, further comprising a speed sensing unit detecting the fan speed and sending a corresponding third electrical signal to the micro-control unit.
 3. The fan speed control system as claimed in claim 1, wherein the humidity sensing element comprises a humidity-sensitive resistor.
 4. The fan speed control system as claimed in claim 1, wherein the temperature sensing element comprises a heat-sensitive resistor.
 5. The fan speed control system as claimed in claim 1, wherein the digital signal comprises a pulse width modulation (PWM) signal.
 6. A fan speed control system, comprising: a fan motor circuit; a temperature and humidity sensing unit detecting environmental temperature and humidity and sending a corresponding first electrical signal; and a micro-control unit receiving and processing the first electrical signal to obtain a digital signal, and sending the digital signal to the fan motor circuit to control fan speed.
 7. The fan speed control system as claimed in claim 6, further comprising a speed sensing unit detecting the fan speed and sending a corresponding second electrical signal to the micro-control unit.
 8. The fan speed control system as claimed in claim 6, wherein the temperature and humidity sensing unit comprises a heat-sensitive element, a humidity-sensitive element, and a plurality of resistors.
 9. The fan speed control system as claimed in claim 8, wherein the heat-sensitive element and the humidity-sensitive element both comprise resistors.
 10. The fan speed control system as claimed in claim 6, wherein the digital signal comprises a pulse width modulation (PWM) signal. 